Communication devices such as wireless devices are also known as e.g. User Equipments (UE), mobile terminals, wireless terminals, terminals and/or mobile stations. Wireless devices are enabled to communicate wirelessly in a communications network or wireless communication system, sometimes also referred to as a radio system or networks. The communication may be performed e.g. between two wireless devices, between a wireless device and a regular telephone and/or between a wireless device and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the communications network.
Wireless devices may further be referred to as mobile telephones, cellular telephones, laptops, or surf plates with wireless capability, just to mention some further examples. The terminals in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another terminal or a server.
The communications network may cover a geographical area which may be divided into cell areas, wherein each cell area being served by an access node such as a base station or network node, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. “eNB”, “eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the terminals within range of the base stations. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the mobile station. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the mobile station to the base station.
A Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the second generation (2G) Global System for Mobile Communications (GSM). The UMTS Terrestrial RAN (UTRAN), is essentially a RAN using Wideband Code Division Multiple Access (WCDMA), and/or High Speed Packet Access (HSPA), for UEs. In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks and UTRAN specifically, and investigate enhanced data rate and radio capacity. In some versions of the RAN as e.g. in UMTS, several base stations may be connected, e.g., by landlines or microwave, to a controller node, such as a Radio Network Controller (RNC), or a Base Station Controller (BSC), which supervises and coordinates various activities of the plural base stations/network nodes connected thereto. The RNCs may be typically connected to one or more core networks.
Specifications for the Evolved Packet System (EPS), have been completed within the 3GPP and this work continues in the coming 3GPP releases. The EPS comprises the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), also known as the Long Term Evolution (LTE) radio access, and the Evolved Packet Core (EPC), also known as System Architecture Evolution (SAE), core network. E-UTRAN/LTE is a variant of a 3GPP radio access technology wherein the RBS nodes, which may be referred to as base stations, eNodeBs or even eNBs, may be directly connected to one or more core networks, e.g., the EPC core network, rather than to RNCs. In general, in E-UTRAN/LTE, the functions of an RNC are distributed between the RBS nodes, e.g. eNodeBs in LTE, and the core network. As such, the RAN of an EPS has an essentially flat architecture comprising RBS nodes without reporting to RNCs. 3GPP LTE radio access standard has been written in order to support high bitrates and low latency both for UL and DL traffic. All data transmission in LTE is controlled by the RBS.
Communications such as transmissions in radio communication systems are often organized in terms of frames, or sometimes subframes, e.g. in LTE, where each frame is a group of communication resources, e.g., radio time and frequency resources, that may comprise both, a control field and a payload data field, or multiple fields of the respective types. A field is understood herein to refer to a set of time and frequency resources, also referred to herein as time-frequency resources. The time-frequency resources corresponding to a field may be contiguous in the time and frequency dimensions. The control field may, e.g., comprise information about how the data part of the frame is encoded and modulated. The control field may also be used for receiving feedback information in the reverse link direction, i.e., from the receiver of the data, e.g., for receiving ACKnowledgement/Negative ACKnowledgement (ACK/NACK) or channel state information reports.
In the wireless communication networks, such as, e.g. UMTS and LTE, both Frequency Division Duplex (FDD), with paired spectrum, and Time Division Duplex (TDD), with un-paired spectrum, may be specified to implement two ways communication with different physical layer frame structures.
An FDD network with symmetric bandwidth in UL and DL, which may be the case in existing systems such as UMTS FDD and LTE FDD, is not spectral efficient when the data traffic volumes in the two directions are not symmetric. The LTE TDD specifies some UL/DL dynamic to increase the spectral efficiency.
In wireless communication networks, a full duplex system is envisioned which may, for example, increase spectral efficiency, decrease latency for un-paired spectrum, and simplify signaling structure of relay networking. However, the existing IEEE 802.11 standards specify only a TDD physical layer frame structure with different frame format to suit the need of data traffic and adapt to carrier frequency.
Half-Duplex
In many radio communication systems, communication nodes may be only capable of half-duplex communication, i.e., a network node, e.g., an Access Node (AN) or a UE, may not both transmit and receive at the same time, at least not on the same frequency band. The main reason for such a limitation is that a network node that is transmitting may saturate its own analog receiving circuitry due to overhearing between transmit and receive antennas.
An implication of this is that data may only be communicated, e.g., transmitted, in one link direction at a time. However, even for one-directional data communication, there may be, as explained above, normally a need for regular communications of control information in both link directions, implying that in half-duplex communications, it may be useful to have two fields for control information in every frame, one for one link direction, and one for the reverse direction. Two fields may be useful also in full-duplex systems, but for other reasons. The two directions of a link will henceforth be referred to as tx/rx directions, or sometimes the two duplex directions. In other words, any given communication node may use one of the fields for transmission (tx) and the other field for reception (rx). The link direction may also be referred to herein as a direction of communication.
Communication as used herein, refers to one of transmission or reception, which may be also referred to collectively as “transmission”, such as a transmission of data or a transmission of control information.
Frame Structure
Examples of frame structures that may be used in a wireless communication network are illustrated in FIG. 1 and FIG. 2. In FIG. 1, a frame structure is disclosed for a minimum subframe or frame unit. The frame comprises at least one control field, i.e. field or set of time-frequency resources to be used for reference signal information and/or control information, which comprises at least one control symbol to be used for transmission or reception. Also, the frame comprises at least one data field for data transmission or reception, i.e. field or set of time-frequency resources to be used for payload data. These are illustrated by the dotted field and the data field in FIG. 1. Here, the control field may be configured to use larger subcarrier spacing and/or zero-padding OFDM to lower overhead for the control field.
According to another example illustrated as a schematic diagram in FIG. 2, cf. also “Time-division duplexing”, WO 2014/121833 A1 (PCT/EP2013/052376), a possible TDD frame structure with three sets of time-frequency resources in a minimum subframe or frame unit and its link-direction assignments is described, in which two sets of time-frequency resources are configured to transmit or receive control information, such as, reference signal information and/or feedback about received transmissions and scheduling information. Here, the other time-frequency resources may be configured for data transmission or reception, which e.g. may be at least 5 times larger than the sum for the other two smaller time-frequency resources. These are illustrated by the dashed control fields and the data field in FIG. 2.
In the two examples above, a frame structure for both FDD and TDD is described wherein the control field is time isolated from the data field and these fields may be controlled to transmit or receive independently, as shown in FIGS. 1 and 2. However, in these examples, two control symbols of the time-frequency resources are reserved for control information. FIGS. 1 and 2 may be OFDM based frame structures.
Any two communication nodes communicating may in principle arbitrarily select which of the two control fields may be used for tx and which for rx, see left and right panels of FIG. 2. However, such arbitrariness may require complicated negotiation procedures and hence it is often more practical to have a general rule for the system, e.g., that one of the fields is always used for DL communication, i.e., tx by ANs, whereas the other field is always used for UL communication, i.e., tx by UEs, see the illustration in FIG. 3 for a schematic diagram of other possible frame structures and respective link-direction assignments. Note also that frames on different links in the system may preferably be time-aligned, partly because this may enable communication nodes to more freely and efficiently change communication partner, that is node, from one frame to another, without waiting for the other communication link to finish its frame.
Fields may, in most transmission systems, be further divided into smaller units, e.g., in Orthogonal Frequency-Division Multiplexing (OFDM) systems, the fields may be further divided into one or more OFDM symbols. A similar principle holds for many other types of systems than OFDM, e.g., for many systems based on multi-carrier or pre-coded multi-carrier such as Filter-Bank Multi-Carrier (FBMC), Discrete Fourier Transform (DFT)-spread OFDM, etc. As a general term, such smaller units may be referred to herein as symbols. Some fields may consist of only a single symbol.
Other Signals and Fields in and Between Frames
Switching of tx/rx direction may take some time, and therefore, may require an extra guard period between adjacent symbols that belong to fields with different duplex direction. Moreover, it should be noted that within the three fields, there may typically also be other signals interspersed, e.g., reference signals, or pilot signals, to allow the receiver to perform channel estimation. For simplicity, guard periods or other signals are not shown in these figures.Self-Backhauling
In the case of radio communication systems with very dense deployment of ANs, as envisioned in particular for systems operating at millimeter-Wave (mmW) frequencies, it may be difficult and costly to provide a wired backhaul connection, that is, a connection with the core network or Internet, to all ANs in the system. One option is to use wireless backhaul, i.e., have one AN with wired connection, henceforth referred to herein as Aggregation Node, or AgN, that forwards data to the other ANs wirelessly over a route, see illustration of a network using wireless self-backhauling in FIG. 4. In the more general case, the routes may form a more complicated pattern, e.g. a route tree. A particularly attractive solution is to use wireless self-backhauling, i.e., use the same frequency spectrum for access links and backhaul links, which avoids the need for multiple radio units in each communication node. Note that in such a network, not only user data may have to be forwarded over the backhaul links, but also control signaling for, e.g., radio resource coordination between ANs, e.g., allocation of time-frequency radio resources and scheduling on access links, or for setting up routes, may have to be performed wirelessly.
Modulation Schemes
OFDM, as a Multi-Carrier Modulation (MCM) scheme may be widely used in wireless communication systems and broadcasting systems, such as, e.g. IEEE 802.11 a/g/n, LTE DL, Digital Video Broadcasting (DVB), etc. . . . . This may enable an efficient implementation and simple transmission and equalization scheme over severe propagation channel conditions, such as, e.g. frequency selectivity. One of the disadvantages of MCM compared to single carrier transmission may be the high peak-to-average-power ratio (PAPR) resulting in higher requirement on the radio frequency hardware (RF HW). To enable low PAPR transmission for wireless devices, a single carrier scheme called DFT-spread OFDM is standardized in LTE UL and as a transmission mode in some of the IEEE 802.11 standards. FIG. 5 is a schematic diagram showing two examples for single carrier localized DFT-spread OFDM. In the Figure, the arrows represent subcarriers wherein signals are being transmitted. The zeros represent that no signals are transmitted in those subcarriers. Thus, the size of the DFT boxes differs, depending on the different number of subcarriers to be transmitted. The bottom drawing shows all subcarriers are used for the transmitter. The top drawing shows only part of the subcarriers are used for the transmitter. Inverse Discrete Fourier Transform is represented as IDFT. FIG. 6 is a similar schematic diagram showing examples of clustered DFT-spread OFDM. A cluster may be one kind of signals, e.g. reference signals may be one kind, control information may be another. FIG. 7 is a similar schematic diagram showing examples of interleaved DFT-spread OFDM, wherein the solid and dashed arrows represent two different clusters.
Furthermore, to also have some flexibility at the same time as keeping a low PAPR property, interleaved—Frequency Division Multiple Access (FDMA) has been proposed as a transmission scheme. FIG. 8 is a schematic diagram showing examples of a regular (left) and a non-regular (right) interleaved FDM. FIG. 8 shows two bars, comprised of boxes with different patterns. Each of the boxes represents a different subcarrier, and the patterns indicate signals of the same kind, e.g., the downward-diagonal pattern represents control information and the upward-diagonal pattern represents reference signals. The left bar represents two kinds of signals are interleaved evenly, and the right bar illustrates an uneven distribution.
To enable gigabit data communication, one way is to use very wideband spectrum in high frequency bands and high gain beamforming with many antenna elements. To keep the HW cost reasonably low, a single-carrier modulation scheme may be used so that the PAPR is kept low and combined with the use of analogue beamforming with a few digital transceiver chains. However, single carrier modulation schemes have a limited flexibility for a combination of multi-user access, self-backhauling and very high-gain beamforming. These are normally considered important issues when considering a future wireless communication networks, e.g. a 5G standard. This is because in such a system, the control information signals may need to be transmitted and received among multiple nodes in different directions.
Also communication networks such as those with very dense deployments of communication nodes, may require exchange of control information among a number of communication nodes, or even all of them, within a certain time period, e.g., a frame. However, current frame structures do not provide support for such communication.